Umami, the fifth basic taste, is igniting interest within the ingredient and culinary worlds. It’s been hailed as savory, delicious, dimensional, and mouth-watering. Food product developers call umami a “back pocket” ingredient—one that supplies the missing link in formulations or recipes. Chefs call umami “yummy” and use terms like “umami synergy” and “u-bombs” to describe the role it plays in food preparation.
“Umami has become one of today’s hottest culinary topics,” says Debbie Carpenter, Senior Marketing Manager, Foodservice and Industrial, Kikkoman Sales USA Inc.
Umami is hardly new. Fermented fish sauces and intense meat and vegetable extracts have been valued in world cuisines for more than 2,000 years (Ninomiya, 2002). Karl Ritthausen identified glutamic acid—the amino acid that elicits a unique umami taste in human sensations—in 1866, and Kikunae Ikeda proposed umami as a separate, distinct taste in 1908.
Umami came of age when Chaudhari et al. (2000) discovered the L-glutamate taste receptor, taste-mGluR4, which regulates the so-called “firing” of taste-receptor cells. Nelson et al. (2002) discovered that a “broadly tuned” amino acid receptor, T1R1+3, was highly stimulated by L-oriented amino acids, such as L-glutamante.
The seasoning monosodium glutamate (MSG) was formulated in Japan in 1909, and introduced into the United States in 1917, which opened a wealth of flavor-enhancement possibilities, according to Brendan Naulty, president of Ajinomoto Food Ingredients LLC.
Shintaro Kodama isolated the nucleotide inosine 5’-monophosphate (IMP), also known as disodium inosinate, from dried bonito tuna in 1913. Akira Kuninaka isolated the nucleotide guanosine 5’-monophosphate (GMP), also known as disodium guanylate, from shiitake broth in 1960, and discovered synergy between glutamate, inosinate, and guanylate. Umami celebrated its 100th year as a separate and distinct taste in 2008.
Herb Bench, Executive Vice President, Nikken Foods Co., USA, says, “Whether intentionally or not, the search for the umami taste has been growing at a rapid pace, driven by the growth of health-related savory foods, such as reduced-salt and low-fat, which generally need flavor enhancement.”
Aside from its own yummy taste, umami alters the perception of other tastes: Sodium seems saltier, sugar sweeter, and sour and bitter less acerbic and biting. Umami also enhances the perception of thickness and complexity and improves the overall palatability of some foods and beverages. Umami has become an increasingly important tool for balancing the five basic tastes, aromas, and textures in product formulation and recipe development.
Umami is found in foods, beverages, and ingredients that are high in amino acids. Foods and beverages at their peak, and those that are aged, dried, cured, fermented, roasted, or toasted are rich in umami. Older animals with very well exercised muscles tend to have more umami, as do fish that are heavy swimmers, such as mackerel, salmon, and tuna. Enzymatic action, naturally occurring or induced through microorganism inoculation, breaks down proteins and releases and boosts umami.
--- PAGE BREAK ---
The taste-active components of umami are due to free glutamate and the nucleotides inosinate (IMP) and guanylate (GMP). Significant levels of free glutamate are found in kombu (kelp), nori (seaweed), Parmigiano-Reggiano, soy sauce, Vegemite, Marmite, fish sauce, monosodium glutamate, oyster sauce, green tea, cured ham, and tomatoes. IMP is plentiful in beef, chicken, dried bonito flakes, pork, sardines, sea urchin, shrimp, snow crab, and tuna. In addition to IMP, beef, sardines, and shrimp also contain glutamate. GMP is abundant in dried shiitake, morel, porcini, and oyster mushrooms, beef, chicken, nori, pork, and snow crab. Drying greatly increases GMP and IMP in shiitake mushrooms and bonito. When raw bonito is dried into katsuobushi (dried bonito flakes), IMP can increase up to 30 times as adenosine triphosphate (ATP) is converted into adenosine monophosphate (AMP). Sources and levels of free glutamate, GMP, and IMP are shown in Table 1.
Unleashing Umami Synergy
Umami synergy characterizes the interaction among free glutamate, IMP, and GMP. It generates amplified and lingering taste sensations— far greater than any single ingredient can create. The extent of the multiplication of the umami taste can be up to eight times the taste of the sum of the separate ingredients (Marcus, 2005).
Major world cuisines have traditionally relied on umami synergy for deliciousness by combining protein foods with IMP and vegetables with glutamate. Examples include kombu (glutamate) with bonito katsuobushi (IMP) and shiitake mushrooms (GMP) in Japanese cuisine; Chinese cabbage and leeks (glutamate) with chicken bones (IMP) in Chinese cuisine; and onions, carrots and celery (glutamate) with beef shanks, poultry carcass, or fish bones (IMP) in Western cuisine.
Umami synergy also comes into play in the popular Western combinations of tomato sauce (glutamate) with meat (glutamate and IMP) in spaghetti with Bolognese sauce and chicken cacciatore; Swiss Gruyère and Parmesan cheese (glutamate) with beef stock (IMP) in French onion soup; anchovies (IMP) with Parmigiano- Reggiano (glutamate) in Caesar salad; and Cheddar cheese with beef (glutamate and IMP) in the ubiquitous cheeseburger.
Umami synergy is intensified by long, slow cooking, such as in double-boiled soups, braises, and daubes, which helps to deconstruct proteins. Searing and roasting protein-rich meats and vegetables before cooking boosts the umami taste even more.
Soy sauce and/or fish sauce with free glutamate can generate umami synergy when products and dishes lack luster. “The addition of soy sauce to such products as canned soups and chilies, poultry products, fajitas, and a variety of jerky products can help food manufacturers create ‘instant umami,’” says Carpenter. “The key to creating umami synergy is balance,” she continues. “In most cases— especially when working with non-Asian foods—you want soy sauce to remain in the background, so that you perceive its complex qualities without actually identifying a pronounced soy sauce taste.”
Unveiling the Umami Taste Mechanism
Our understanding of the umami taste transduction mechanism is still in its infancy. The umami taste is perceived through a receptor-mediated mechanism. The synergistic interactions between glutamate, GMP, and IMP increase from an allosteric effect of these nucleotides on glutamate receptors (Fuke and Ueda, 1996). The proportion of L-glutamate to nucleotides is important in umami synergy.
--- PAGE BREAK ---
Li et al. (2008) proposed that the T1R1 taste receptor is shaped like a Venus flytrap. The L-glutamate receptor binds inside, and the “flytrap” closes around it. The 5’ribonucleotides bind on an adjacent site and further stabilize the conformation, which allows glutamate to stay in the “mouth” of the receptor longer. This coupling produces a “metabolic cascade” of neurotransmitters that transmit signals to the brain’s sensory cortex where the umami taste is perceived. It may also allow taste researchers to clarify taste preferences.
Age and food habits appear to be the most important factors that determine umami taste perception (Iordachescu, 2008). Breslin et al. (2009) demonstrated variations in genes that code for T1R1 and T1R3 correspond to individual variation insensitivity to the perceived intensity of the umami taste.
Umami's Prospective Role in Flavor Enhancement
Umami’s role as a natural flavor enhancer is well documented. The amount of salt in a food product that is perceived to be satisfying ranges from 0.6-1.0% (Takahasi, 2009). Fuke and Udea (1996) conducted one of the most comprehensive studies that showed how umami could replace salt in food yet retain taste appeal. A traditional Japanese dish, katitamajiru (dashi-based soup with beaten egg), was prepared with a table salt content of 0.6%; usukuchi shoyu (light soy sauce) content of 0.5%; and an overall salt content of 0.7%. By replacing salt with umami in the form of monosodium glutamate (at a concentration of 0.04%), the total sodium content was lowered by 30%.
Beauchamp et al. (1998) demonstrated that MSG increases the palatability of salted soups and that both sodium and glutamate independently contribute to this flavor enhancement. Subjects preferred soups with monosodium glutamate when salt levels were low to moderate.
New GMP derivatives may enhance the sensorial impact of monosodium glutamate (MSG) and boost the umami taste in savory foods. Cairoli et al. (2008) investigated the potential of N2-alkyl and N2-acyl derivatives of GMP that synergistically react with MSG. The enhancements (1.2 to 5.7) were greater than the enhancement of MSG and IMP (1.0). The enhancing capabilities of GMP derivatives were related to the chain length of the alkyl or acyl substituent.
Umami’s Potential Role in Reducing Dietary Sodium
Salt has been under increased scrutiny due to its relationship to hypertension, a major risk factor in cardiovascular disease. One teaspoon of common table salt contains about 2,400 mg of sodium. The 2005 USDA Dietary Guidelines has established a total daily sodium intake level of 2,300 mg. It is estimated that the average U.S. salt intake is about 1½ times this amount, with up to 75% from processed foods, condiments, canned foods, and prepared mixes (CDC, 2009).
The American Heart Association recommends that sodium intake be reduced to 1,500 mg daily for salt-sensitive populations. A recent study by Stamler et al. (2009) concluded that dietary glutamic acid may have independent blood pressure–lowering effects, which may contribute to the inverse relation of vegetable protein to blood pressure.
--- PAGE BREAK ---
There are three main issues when sodium is reduced in processed foods: taste, processing, and preservation. Reduced-sodium products tend to be bland, with less initial impact and expansion. Less protein is extracted in meat processing when sodium is reduced, and there are changes in food chemistry. Since salt helps preserve food, reduced salt may shorten a product’s lifespan.
Potassium chloride, reduced-sodium preparations, and umami (in the form of monosodium glutamate, sodium-free glutamates, nucleotides, and yeast extract/HVP) offer reduced-sodium applications. On a per weight basis, monosodium glutamate is naturally low in sodium (sodium is 11.3% of the compound weight compared with 39.4% in salt). Proper use of the umami taste could contribute up to a 50% salt reduction without compromising consumer acceptance (Marcus, 2005).
The glutamate taste is intensified when combined with some sodium in cooking. Salt a tomato and it tastes more “tomato-ey.” It also tastes multidimensional: You can detect the other basic tastes, plus a savory, brothy, mouth-filling sensation. Roasting tomatoes furthers this dimensionality.
Some ingredients add instant salty/bitter/umami notes; have the potential to decrease the total sodium in formulations and recipes; and add depth of flavor if used sparingly. These include anchovy powder, fermented black beans/bean paste, fish paste and fish powders (especially those with reduced fish tastes), mushroom powder, Parmesan cheese, seaweed, soy sauce, tomato powder, and Worcestershire sauce.
“When food manufacturers look to reduce sodium content, umami can help them retain the savory taste, while they still retain ‘craveability.’ Naturally brewed soy sauce, with more than 300 distinct flavor and aroma components, is one of the most versatile, all-purpose umami ingredients for reduced-sodium and reduced-fat applications, and can add zip to low-fat foods,” says Carpenter.
Lower-sodium soy sauce begins as regular soy sauce; then filtering or ion exchange removes some sodium. After the natural brewing process is complete, Kikkoman uses a proprietary dialysis process to remove 37% of the salt, while all of the umami-enhancing ability is left intact. Cutting back on the salt in soy sauce lets some of the other distinct flavors advance and brings a delicate, complex soy taste to the foreground. Once cooked, these delicate flavors disperse.
Autolyzed and hydrolyzed yeast and yeast extracts, hydrolyzed and texturized proteins, monosodium glutamate—a natural source of umami, and refined forms of amino acids and nucleotides, which overcome control issues without bulk, color, and other potentially undesirable flavor notes, also present a wide range of reduced-sodium product and recipe possibilities.
Umami’s Promising Role in Reducing Dietary Fat
Western diets often rely on fat for flavor. Like sodium, too much fat has health ramifications. Diets that are low in flavor, variety, and intensity tend to fail. Obese people have different orosensory and orohedonic experiences than non-obese. They experience reduced sweetness, which probably intensifies fat sensations, and like both sweet and fat more than the non-obese (Bartoshuk et al., 2006). The savory nature of umami helps create a fullness of taste that people perceive as mouthfeel or texture.
--- PAGE BREAK ---
“Umami ingredients make foods taste richer and more fully rounded,” Carpenter explains. “Lean proteins usually have reduced flavor (from less fat), so the addition of umami-rich ingredients, such as soy sauce, provides the synergies needed to compensate for what may be lacking.”
Kokumi is another option for reduced-fat applications. Well-known in Asia, though relatively unknown in the U.S., kokumi is characterized by a blend of initial flavor impact, continuity, and roundness. “Think of kokumi as “umamiplus”— the umami taste plus an increased sense of mouthfeel and texture,” explains Naulty.
Ajinomoto Food Ingredients produces two kokumi enhancers: SuperYE and Koji-aji. SuperYE is a proprietary blend of special yeast extracts that deliver required peptides plus umami. Rich, heavier flavors, such as beef and pork, are most compatible; products featuring cheese or wine flavors can also benefit. Koji-aji, a blend of fermented wheat protein and yeast extract, works best with chicken, seafood, vegetable, and cheese-based applications.
Surprisingly, fruit can lend an umami-type texture to protein foods—such as how pork softens and expands when it is roasted in apple cider. The fruit pectin adds a lubricity to meat, giving it mouth-satisfying texture, along with the meat’s natural umami.
Umami-rich wine is also an important ingredient in low-fat cooking. Wine contains umami from fermentation, along with alcohol, a powerful flavor extractor. Alcohol dissolves both water-soluble and fat-soluble flavors. This feature is important in reduced-fat cooking, since alcohol tends to hang on to flavor—especially umami, while it brings out other flavors. In lower-sodium formulations, wine powder adds depth of flavor without the alcohol.
Umami’s Possible Role in Appetite Regulation and Satiety
We are innately programmed to seek the umami taste when we are hungry—protein satisfies our need for sustenance. When we are sated, we are less driven to seek protein—that’s why the umami taste may be helpful in the battle of the bulge.
In addition to the oral cavity, umami is detected by umami receptors and a glutamate-sensing system throughout the gastro-intestinal tract. The gastric afferent branch of the vagus nerve reacts only to glutamate. This suggests that when food enters the stomach and glutamate receptors detect the presence of umami, this information is relayed to the brain by the gastric vagal afferent, which alerts us to the presence of umami. Then a message is sent from the brain back to the gastro-intestinal tract to digest proteins. This taste awareness is crucial to our health and wellbeing since it drives us to select foods that we need for survival (Takahashi, 2009).
The very satisfying nature of umami also plays a role in appetite regulation. A little bit of great-tasting food or beverage with umami is an important consideration in determining how much food we eat at a sitting and has great potential in weight management. This phenomenon is referred to as “sensory-specific satiety.” Rolls et al. (2003) monitored the brain activity that controls the appetite of people who consumed umami-rich tomato juice. When consumed to satiety, their “pleasantness rating” decreased, as noted in the orbitofrontal cortex—the region of the brain that controls appetite.
Flavor enhancers and aromas with umami may also be able to alter the sensory impact of food, satiety, and food intake behavior. In rats provided with water and/or a 1% monosodium glutamate solution with diets of varying caloric density, fat, and carbohydrate content for 15 weeks, fluid and glutamate intake was higher in the MSG-fed rats, and MSG-consuming animals had lower body weight, intra-abdominal fat mass, and subcutaneous fat mass, suggesting that umami-rich foods may help reduce weight gain and fat deposition (Kondon and Torii, 2008).
--- PAGE BREAK ---
Chefs and the Umami Table
Chefs from around the globe are incorporating the umami taste into their cooking with excellent results. Heston Blumenthal (The Fat Duck, Berkshire, UK); Jonathan Pratt (The Umami Café, Crouton-on-Hudson, N.Y.); and Yoshihiro Murata (Kikunoi, Kyoto, Japan) are longstanding umami enthusiasts.
At the 2008 Japanese Culinary Fellowship Workshop in Kyoto, Japan, Chefs Michael Anthony (Gramercy Tavern, New York City); David Chang (Momofuku, New York City); Mauro Colagreco (Mirasour, France); Claude Bosi (Hibiscus, UK); and Sat Bains (Restaurant Sat Bains with rooms, UK), prepared single-dish culinary creations that featured umami-rich ingredients. Chef Bains prepared pork, large prawns, cauliflower, and persimmon seasoned with kombu dashi, yuzu citron, and Marmite. Chef Bains discovered the umami taste to be indispensable in his cooking. His journey emphasizes how chefs are appreciating and utilizing the functionality of umami in their cooking.
Bains first discovered umami about nine years ago, but his real insight into the versatility of umami occurred during this workshop. He discovered umami through dashi, and the entire balance of the kaiseki meal (the traditional multi-course Japanese dinner analogous to Western haute cuisine).
Working with umami has allowed him to move into a healthier, more natural direction by using cleaner flavors. Bains was interested in lowering salt in his cooking to let ingredients shine on their own merit without over-seasoning. By using umami, Bains has reduced salt by as much as 30%.
To achieve “umami hits,” Bains uses umami-rich ingredients such as dashi, Marmite, roasted tomato seeds and skins, kombu, Parmesan cheese, roasted meat bones, bonito flakes, and fermented fish. Bains prefers ingredients that carry a depth of flavor without underlying flavor notes.
One of the most popular dishes Bains features is beef cheeks with seaweed and oysters—a perfect example of glutamate, IMP, and GMP synergy. This dish typifies Bains’ approach of balanced seasoning using umami as a base taste and for bringing out other tastes.
Bains brines beef cheeks overnight in a kombu base solution. He adds aromatics, beer, and honey, and lets the mixture infuse for three days for flavor absorption and tenderizing. Then he sears the meat to create more umami through roasted flavor notes, and reduces the liquid for more depth of flavor, and then adds it back to the beef cheeks. Strips of kombu are added, and the mixture braises overnight or until tender.
Pickled onion juice is combined for acidity and balance, along with bonito flakes for another “umami hit.” The mixture then sets to absorb the smoky flavor and is re-seasoned with just a touch of salt—only if necessary. Chef Bains completes this dish with an oyster emulsion, accompanied by a fresh seaweed and bean sprout salad, as pictured on page 35.
Besides salt reduction, another quality of umami, says Bains, is its ability to lower the fat in his cooking. By adding umami strategically throughout his tasting menu, Bains says he can dictate the path toward fullness without overfeeding his guests.
--- PAGE BREAK ---
Recent Umami Applications
Umami-centered foods may help stretch more expensive ingredients, lower production costs, and provide better value for the consumer. Lower-sodium nucleotides in combinations with vegetables help bring out flavor, create umami expansion and harmony, and reduce bitterness. For the percentage of people who are highly sensitive to the bitter taste, umami smoothes out the bitterness in coffee and tea.
“Although umami isn’t unique to Asian foods,” says Carpenter, “the explosion of interest in Asian cuisine will only create increased opportunity for food manufacturers to use soy sauce to enhance umami. Some examples of the unexpected are frozen dinners, snack foods, and chocolates.”
Other than soy sauce, anchovy powder, cheese powder, mushroom powder, and fermented soybean paste have been used in vegetable and fruit crisps in Asian and Latin American applications. Chocolate ice cream syrup, with reduced-sodium soy sauce and cocoa powder, has been used to depress the extra sweetness of typical ice cream syrups, enhance the richness of the cocoa, and produce a deep, nutty, roasted chocolate flavor. Nucleotides contribute fullness to chocolates. Reduced-fat formulations can replicate some aspects of the mouthfeel and texture of chocolate— not just physical viscosity, but the taste of chocolate, as well. Alapyridaine, a tasteless compound isolated from beef stock that relies on GMP synergism, augments salty, sweet, and umami flavors in food, and helps make bitter chocolate taste sweeter.
Future Umami Applications
Geographic, economic, and religious constraints may limit diets. Grains, roots, tubers, legumes, and starchy fruits help satisfy minimal nutritional needs, yet they tend to be unpalatable in the long term. Flavor enhancement with umami can supply meatiness and boost appeal in diets that include little meat and other proteins. Worldwide applications of the umami taste are shown in Table 2.
It is well documented that the sense of taste and smell wanes during the aging process (Schiffman et al., 1993). A number of studies have examined the potential usefulness of l-glutamate, added to food in the form of monosodium glutamate (MSG), in promoting better nutrition in the elderly and in patients with poor nutrition. Some positive effects have been observed (Yamamoto et al., 2009).
In a recent study by Tomoe et al. (2009), hospitalized elderly patients received supplementation of 0.5% MSG added to 150 g of rice meal, served three times daily for 3 mo. Behavior during mealtime and nutritional status improved.
“Increased focus on ‘better-for- you products’ will demand that manufacturers find ways to maintain the flavors of foods while reducing, sodium, fat, and calories,” Carpenter says.
According to David Adams, President, Savoury Systems International Inc., “There can be more applications of umami in the snack food area and high-sodium deli meat.”
“There is little downside to incorporating umami in new products,” says Bench. “There is still much to learn about how to build umami in many food formulations. The expertise is rapidly growing. Also, as more chefs experiment with umami building we will see many exciting new recipes in the restaurant and foodservice industry.”
Bartoshuk, L.M., Duffy, V.B., Hayes, J.E., Moskowitz, H.R., and Snyder, D.J. 2006. Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives. Philos. Trans. R. Soc. B. Biol. Sci. 361(1471): 1137–1148.
CDC. 2009. Application of lower sodium intake recommendations to adults—United States 1999-2006. Morbidity and Mortality Report 58(11): 281-283. U.S. Government Printing Office, Washington, D.C.
Chaudhari, N., Landin, A.M., and Roper, S.D. 2000. A metabotropic glutamate receptor variant functions as a taste receptor. Nat. Neurosci. 3(2): 113-119.
Chen, Q.-Y., Alarcon, S., Tharp, A., Ahmed, O.M., Estrella, N.L., Greene, T.A., Rucker, J., and Breslin, P.A.S. 2009. Perceptual variation in umami taste and polymorphisms in TAS1R taste receptor genes. Am. J. Clin. Nutr. 90(3): 753S-755S.
Cairoli, P., Pieraccini, S., Sironi, M., Morelli, C.F., Speranza, G., Manitto, P. 2008. Studies on umami taste. Synthesis of new guanosine 5’-phosphate derivatives and their synergistic effect with monosodium glutamate. J. Agric. Food Chem. 56(3): 1043-1050.
Fuke, S. and Ueda, Y. 1996. Interactions between umami and other flavor characteristics. Trends Food Sci. and Technol. 7(12): 407-411.
Iordachescu, G., Vlasceanu, G., Bleoanca, I., Neagu, C., and Iordachescu, A. 2008. Umami taste and the consumer perception. The Annals of the University Dunarea de Jos of Galati Fascicle VI, Food Technol., New Series Year II (XXXI): 58-61.
Klebansky, B., Fine, R.M., Xu, H., Pronin, A., Liu, H., Tachdjian, C., and Li, X. 2008. Molecular mechanism for the umami taste synergism. PNAS 105(52): Article #08-10174.
Kondoh, T., and Torii, K. MSG intake suppresses weight gain, fat deposition, and plasma leptin levels in male sprague-dawley rats. Physiol. Behav. 95(1-2): 135-144.
Kringelbach, M.L., O’Doherty, J., Rolls, E.T., and Andrews, C. 2003. Activation of the human orbitofrontal cortex to a liquid food stimulus is correlated with its subjective pleasantness. Cereb. Cortex 13(10): 1064-1071.
Labarthe, D. 2009. Report: U.S. Institute of Medicine Meets on Salt Reduction January 2009. Presented at the Institute of Medicine Committee on Strategies to Reduce Sodium Intake. Miami, Fla., Jan. 13-14.
Marcus, J.B. 2005. Culinary Applications of Umami. Food Technol. 59(5): 24-30.
Nelson, G., Chandrashekar, J., Hoon, M.A., Feng, L., Zhao, G., Ryba, N.J., and Ninomiya, K. 2002. Umami: A universal taste. Food Rev. Intl. 18(1): 23-38.
Okiyama, A. and Beauchamp, G.K. 1998. Taste dimensions of monosodium glutamate (MSG) in a food system: role of glutamate in young American subjects. Physiol. Behav. 65(1): 177-181.
Schiffman, S. S. and Gatlin, C. A. 1993. Clinical Physiology of Taste and Smell. Annu. Rev. Nutr. 13: 405-436.
Stamler, J., Brown, I.J., Daviglus, M.L., Chan, Q., Kesteloot, H., Ueshima, H., Zhao, L., and Elliott, P. 2009. Glutamic acid, the main dietary amino acid, and blood pressure: the INTERMAP Study (International Collaborative Study of Macronutrients, Micronutrients and Blood Pressure). Circ. 120(3): 221-8.
Takahasi, Y. 2009. “Dashi and Umami: The Heart of Japanese Cuisine.” Eat-Japan/Cross Media Ltd., London, UK.
Tomoe, M., Inoue, Y., Sanbe, A., Toyama, K., Yamamoto, S., and Komatsu, T. 2009. Clinical trial of glutamate for the improvement of nutrition and health in the elderly. Ann. N. Y. Acad. Sci. 1170: 82-6.
Yamamoto, S., Tomoe, M., Toyama, K., Kawai, M., and Uneyama, H. 2009. Can dietary supplementation of monosodium glutamate improve the health of the elderly? Amer. J. Clin. Nutr. 90(3): 844S-849S.
Zuker, C.S. 2002. An amino-acid taste receptor. Nature 416: 199-202.